1. Field of the Invention
The invention relates to pile driving, and more particularly, but not exclusively, to underwater pile driving, e.g. for stabbing piles directly into the seabed.
2. Description of the Background Art
It is known to provide a guide for aligning a pile with the surface of a substrate into which the pile is to be driven and to provide stability for a piling hammer. Particularly when piling underwater there is the problem that after the pile has been introduced into the seabed or the like, the guide must be removed to allow the pile to be driven into its final position. This guide removal is time consuming and thus expensive. Accordingly, the present applicant proposed in International patent publication WO99/11872 a pile guide which allows pile driving to continue from start to finish without any need to interrupt driving to remove the guide. However, the pile guide disclosed in WO99/11872 may not be suitable with relatively short piles (less than 20 m in length) because a laterally protruding coupling for a tether located at the trailing end of such piles fouls the pile guide before a sufficient length of pile is embedded in the seabed to ensure stability.
In practice, it may also be important to orientate the pile so that its laterally protruding coupling will be aligned in a predetermined direction according to the intended use of the pile. A set pile orientation may be achieved using so-called orientation plates on the piles which engage a guide plate system in the pile guide member of the pile guide. The orientation plates are positioned on the piles in a known orientation relative to the tether/riggings couplings provided on the piles. In use, the orientation plates will engage the guide plate system as each mis-orientated pile is introduced into the pile guide member. The guide plate system forces the orientation plates to follow a helical path as the pile is further lowered through the pile guide member, causing the pile to rotate about its axis until the desired orientation relative to the base frame is achieved.
The present applicant has appreciated the need for a pile guide system that allows piles with laterally protruding couplings to be driven into a substrate, at least to a point where they are self supporting and stabilised, without fouling the pile guide.